Sextant



Filed oct. 4, 1949 Sept. 22, 1953 v P. F. EVERITT ET Ax. 2,652,976.

` sExTANT 4 Sheets-Sheet l A 'Inemora Sept. 22, 1953 P. F. EVERITT ETA1.

SEXTANT 4 Sheets-Sheet 2 Filed Oct. 4.' 1949 L///A/ 1 j A! omeys Sept.22, 1953 P. F. EvERlTT ET AL v 2,652,975

' SEXTANT Filed Oct. 4. 1949 4 Sheets-Sheet 5 38 F/Gj4.

| WHHHII HHH' Sept. 22, 1953 Filed oct. 4. Y1949 P. Fu EvERlTT ET AL2,652,976

4 Sheets-Sheet 4 Patented Sept. 22, 1953 SEXTANT Philia.FltancisgEvetitt, Seven Kingapandj A.lohn Keeble, Ilford, England,assignors, by-mesne lassignments, to Kelvin & Hughes Limited', Glasgow,a British company -Anlllicationzctolmn 4, 1949,*Se1iaLNoeLl9AS3 In GreatBritain October 5,1948

3 Claims.

1 'Ihis invention relates to., sextants of the kind in which anintegrating: device. gives an average of continuous readings. Itfhasbeen proposed to `provide such anfarrangmentain:which concentric discdials are provided to give the required readings at one side of theinstrument while other readings are observed through windows in anadjacent side of the instrument.

The main object of the present invention is to provide a device in whichthe mechanism is of simpler construction than heretofore and allreadings can be taken from one side of the instrument e. g. at rightangles to the sighting telescope. i

According to the invention an integrating device has a cone which drivesa cylinder through one or more ballsrcarried iria cagethat, isv drivenalong the cylinder, and the cylinder is geared to a shaft which carriesthe cone rotatably thereon, and a series of live-.drums are mountedaround the shaft and marked on their peripheral surfaces, two indicatingdegrees and minutes of altitude respectively and the other three beingintegration `aligning drums, two of which are connected respectively tothe shaftandthe, cone and are geared by differential gearing to thethird, the arrangementbeingsuch that after use the three integrationdrums are reset to their initial positions the' otherdrums directlyindicate the average altitude.

Thus the; markings on the drums can all be read from one side of theinstrument, and a Asimple andV reliablev mechanism is used.

A constructionalform of theeinvention will now be described by way ofexample with reference to the accompanying diagrammatic drawingswherein:

Figure lis; a view partly inv vertical section and partly in, elevationofv a periscopic sentant made in` accordanceA with `the invention;

Eigurez is a vertical sectional view of., the integrating mechanismshown in elevationin Eigure 1,;

Figure 3 is a sectionalfvew on theline 3-3 Qn/FigureZ'vwith certainparts (a counter-shaft and parts carried thereby)` removed;

,Figure 4 is a sectionalview on the line Li-ll on lligure 2;

Figure 5 is a perspective view of al detail shown in Figure 2;

,Figure 6 is-an axialview of thepar-ts shown inFigure drawnfto, asmallerscale; and

Eigure.- 7. is a` sectonalfviewon the ,line '1 -1.. on yliigureG.

The; sexta-nt casingehas I abort-like. part I li-and a periscopic tubeII and an eyepiece telescope 9.

In theupper'end of" the tube II is mounted a sighting prismI-2adjustable by means of an arm I3 the lower endl of'which is fixed toa nut I'4 on a micrometer -screw I5 associated with an anti-backl lashnut IS. Thus the means comprisingV the prism I2 is adjustable by thescrew I5 according to observed altitude. The screw I5 is carried by aspindle I1 which carries a worm-wheelv I8 driven by worm I9 which inturn is driven by an electricv motor 20 through a reversible drivecontrolled by any suitable switch and'nger control sothat the-operatorby driving in one direction or the otherv when required` can adjust theprism according to observed altitude by retaining the heavenly bodyunder observation in the eyepiece telescope.

The spindle I1 also carries a pinion 2I, having a Vback-lash adjuster23, in mesh with a gear- Wheel 22V thatv is fixed to-a sleeve 24 thatcarries a cone 25'that is fixed to the sleeve 24. The cone is carried;in bearings 26, 2l, and supports a spindle 2S on which it is Vfreelyrotatable.

Y".ll'ie conedrives balls 3Q, whichdrive-a cylinder 32 carried on aspindle 33 whichv carries a gearwheel 3ft` inmesh with a pinion 35, andbacklash adjuster 35', on the spindle or countershaft 2S.

The spindle 33 Vis mounted in a bracket 38 that is pivotally supportedon hardened cones 3S, 45 V(Figure 4*). A leaf spring 4I presses on thebracket to hold the cylinder against the adjacent `ball 33. The balls353' are carried by a. cage '42 `to which is attached arack 44 driven bya motor and pinion (not shown) at a constant speed.

Five-reference drums I, 2, 3, 4, 5 are;k provided side by side andcoaxial with the spindle 28., They can allbe seen through one or moreappropriate openings or windows in one side of the box Ifii. The drumsI, 2, 3, all carry markings such asA, B, C, etc., to facilitateresetting them to their initial or zero positions. Thedrums @and daremarked inr degrees and minutes of altitude respectively.

Looking-at the sighting windows the drums are I, 2, 3, the integrationaligning drums; No..A 4 thedegree indicating drum, and No. ithezminuteindicating drum. No. I is secured to the aforesaid shaft`28 and No. 3and No. 5 are mountedon the sleeve 24. attached to the cone. Two drums 3and 5 are provided because 3 carries alignment markingsA and 5 carriesminute markings which is more convenient than having both setsofmarkingson one drum. No. I carries pinions 6 meshing with a sun-wheel'l carriedamf` `the sleeve 24 and with a sun-wheel 8 carried by drum 2,the rst sun-wheel having one tooth less than the other sun-wheel so thatdrum 2 has differential movement. Drum 4 is carried freely and driven bya gearing device 9, mounted on an eccentric 48 on the sleeve 24, andconnected to a fork 4'I engaged by an eccentric 49 on the end of thespindle I1. The device 9 consists of inner and outer pinions the innerone having one tooth less than the outer pinion. The outer wheel movesone tooth for every revolution of the eccentric 48. The gearing 9, 41,48, 49, is of known type sometimes called a two-gear clock mechanism.The inner of the pinions 9 must be restrained from rotating. one end tothe inner pinion and prevents the inner pinion from rotating. Movementof the eccentric 48 causes the inner pinion to move eceentrically sothat its teeth engage progressively with the teeth of the outer of thepinions 9. As there is one tooth less on the inner pinion than the outerpinion, the latter moves round one tooth for every revolution of theeccentric 4t. The eccentric d keeps the inner pinion with the upmpermost tooth always uppermost. Without the eccentric lil the uppertooth would oseillate oil dead centre corresponding to the rockingmotion of the fork- 4l. Drums 2 and 4 are freely mounted on the sleeve2d and drums 3, 5 are fixed on 'the sleeve 24.

The operation or the device is as follows:

The operator precomputes the approximate altitude of the heavenly bodyto be observed, and sets the computed figure on drums 4 and 5 byoperating the motor 2S. This will not affect the drums I, 2 and 3because the rack 44 will be stationary and the ball drive 3ft will be atthe left hand end or Figure 2 giving a lzl drive ratio between the cone25 and the cylinder 32. Then he sights the heavenly body and starts thedrive to the rack 44 which advances uniformly. Duringthe movement of therack fifi. he continues to maintain the heavenly body in the telescopeeyepiece sight by operation oi the motor 2t whereby the cone is drivenvariably as controlled by the the operator and whereby motion accordingto the sighting angle is applied through sleeve 21; to the drum 3 and isalso applied through the cone, balls, cylinder, and spindle 2t, to thedrums i and 2 this motion being varied according to the position of theballs along the cone; at the same time the drum 5 is driven from thesleeve 24 and the drum 5 drives the drum 4 through the two gear clockmechanism. After any period of reading the integrator drums i, 2 and arereset to bring their zero marks into alignment by operating the motor 2@and screw l5 (without yet returning the rack 4t), and the average altitude is then directly indicated by the drums 4 and 5.

It is not necessary to return the drums 4, 5, to their originalpositions as they can start from any position. The drunis i, 2 and 3 andrack 44 are nally brought back. to their normal positions with thesedrui .s in alignment and the instrument is then ready to start a freshoperation.

The invention may be used in conjunction with the invention described inthe speciiications of applications of even date Nos. 119,492-45.

Theory of integrator The action or" the above described mechanism is asfollows:

Suppose the gear ratio between the cone and the cylinder at time t is(A-i-Kt) The fori; 4l is fixed atdH(A-|-Kt) Then if A=1 i. e. theinitial gear ratio being 1:1

- Vthe relative movement of the cone and cylinder is icv Then, over aperiod of integration the total relative movement is H L Ki+dH Now, therequired average altitude H'ab Integration by parts:

Where H1 is final altitude at time T.

Then

Thus the average consists of the iinal altitude minus an amount H L KtdHthe drums I, 2, and 3"into alignment since the misalignment H 0 KtdH andrelative gear ratio is KT.

We claim:

l. A sextant having a cone, means for driving the cone in accordancewith observed altitude, a cylinder, a ball device for driving saidcylinder from said cone, means for traversing the ball device along thecone and cylinder, a shaft on which the cone is rotatably mounted forindependent rotation, means for driving said shaft from said cylinder,iive drums mounted for rotation about the axis of said shaft and markedon their peripheral surfaces so that two of said drums indicate minutesand degrees of altitude respeo tively and are driven from the cone, theother drums beingintegration aligning drums, the first of saidintegration aligning drums being attached to said shaft, the secondbeing connested to and driven by the cone, and the third being freelymounted for receiving differential rotation from the first integrationaligning drum and the cone.

2. A sextant as claimed in claim l having a micrometer screw parallel tothe axis of the cone, a reversible motor reversible means for drivingthe screw from the motor, means adjustable by the screw according toobserved altitude, and

gear wheel connecting the screw and cone.

3. A sextant as claimed in claim 1 wherein said References Cited in theme of this patent means for driving the cone includes an electric motor,a spindle, a worm and worm-wheel driv- UNITED STATES PATENTS ing saidspindle, a sleeve, and gearing connec- Number Name Date tions betweenthe sleeve and spindle, said sleeve 5 2,140,579 Gray Dec. 20, 1938carrying the cone and the minute indicatingv 2,431,555 Wodalef, a1 Sepa,13, 1949 drum, and a reduction device conveying motion from the spindleto the degree indicating drum FOREIGN PATENTS to provide the operativeconnection between said Number Country Date degree indicating drum andsaid means for driv- 10 590 164 Great Britain July 10s 1947 ing the00ne- 603706 Great Britain June 22 1948 PHILIP FRANCCIIS EVERITT. JOHNKEEBLE.

